It is generally considered that the pathogenesis of progressive, delayed death of nerve cells, observed in cerebral injury and cerebrovascular disease such as intracerebral hemorrhage, transient ischemia attack, and cerebral infarction, is mainly caused by a rise in intracellular Ca2+ concentration due to various factors related to signal transductions. Such factors related to signal transduction include, for example, abnormal activation of glutamate receptors due to excessive release glutamate, that is, an excitatory neurotransmitter, abnormal activation of ion channels, and excessive production of reactive oxygen species/free radicals. [F. B. Meyer, Brain Res. Rev., 14, 227 (1989); E. Boddeke et al., Trends Pharmacol. Sci., 10, 397 (1989); J. M. McCall et al., Ann. Rep. Med. Chem., 27, 31 (1992)].
From these points of view, medicaments for preventing or suppressing the neuronal cell death, such as glutamate receptor antagonists, calcium channel blockers, antioxidants and so on have been developed. However, these clinically used medicaments suppress only a few pathways related to increase of the cellular Ca2+ concentration, and are not sufficient for preventing or suppressing the neuronal cell death.
On the contrary, calbindin D28Kd, one of Ca2+-binding proteins and mainly distributed in friable site of the brain against ischemic disease, is reported to possess buffering effects for a rise in cytotoxic intracellular Ca2+ concentration. [A. M. Lacopino et al., Neurodegeneration, 3, 1 (1994); M. P. Mattson et al., Neuron, 6, 41 (1991)]
Accordingly, it is expected to achieve sufficient neuroprotective effects against the increase of intracellular Ca2+ concentration caused by any kinds of pathways if calbindin D28Kd, one of the Ca2+-binding proteins per se, can be supplied in a living body. That is, it is expected that medicaments containing calbindin D28Kd would be effective therapeutic and improving agents for the allevivation or treatment of symptoms due to various ischemic disorders in the brain such as sequelae of cerebral infarction, sequelae of intracerebral hemorrhage, sequelae of cerebral arteriosclerosis and so on, and symptoms of organic brain disorder such as senile dementia, sequelae of head trauma, sequelae of surgical brain operation, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and so on.
However, because calbindin D28Kd is unstable macromolecular protein having 28 Kd (kilo dalton) of molecular weight, it is difficult to be administered directly into a site in the central nervous system of a living body in view of pharmacological and pharmaceutical standpoints.
On the other hand, the lower molecular compounds having effect on induction of the calbindin D28Kd can be easily prepared into the various kinds of pharmaceutical compositions by the conventional techniques. Thus, these lower molecular compounds are expected to induce the calbindin D28Kd after administration in to a body, and to possess buffering action against the increase of the cellular Ca2+ concentration. That is, these lower compounds can be effective compounds for improving and treating cerebral functional and organic disorders.
Under these circumstances, the objective of the present invention is to provide the lower molecular weight compounds having neuroprotective effect by inducing the calbindin D28Kd, one of Ca2+-binding proteins, of low toxicity in suitable preparations of pharmaceutical compositions such as intravenous injectable solution.
The further purpose of the present invention is to provide the therapeutic and improving agents for the allevivation or treatment of symptoms due to various ischemic disorders in the brain such as sequelae of cerebral infarction, sequelae of intracerebral hemorrhage, sequelae of cerebral arteriosclerosis and so on, and symptoms of organic brain disorder such as senile dementia, sequelae of head trauma, sequelae of surgical brain operation, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and so on.